1. Field of the Invention
The present invention relates to a polishing system for flattening the surface of a semiconductor apparatus by mechanical and chemical polishing, adapted for use, for example, in a lithographic process for obtaining semiconductor apparatuses of a high level of integration by flattening the surface of an insulation layer applied on a silicon substrate by effecting the polishing always with a constant polishing rate while monitoring the degree of the polishing surface of the polishing pad used for the polishing operation.
2. Related Background Art
The recent advances in the level of integration of the semiconductor apparatuses have stimulated the progresses toward the finer design of the circuit patterns and toward the three-dimensional structure of the apparatuses. The depth of focus of the projection optical system is reduced as the numerical aperture thereof is increased for realizing the higher level of integration of the semiconductor apparatuses. For this reason, it is important to obtain a high resolution by flattening the surface of the semiconductor apparatus with a polishing operation, thereby eliminating the step difference or the irregularities on the surface, and applying and exposing the photoresist on the thus flattened surface.
The polishing of the insulation layer formed on the silicon substrate for obtaining the layer of a uniform thickness is an important factor for minimizing the fluctuation in the interlayer capacitance and obtaining the through holes of a constant depth.
Mechanical and chemical polishing has conventionally been proposed as the flattening technology for eliminating the surface irregularities and the step differences of the semiconductor apparatuses.
For performing efficient polishing in such mechanical and chemical polishing, it is necessary to adequately control the surface condition (degree) of the polishing surface of the polishing pad, the slurry concentration of the polishing liquid, the temperature of the polished surface, etc. Under unsatisfactory control of these conditions, the desired amount of polishing will not be performed even after passing of the predetermined polishing time, and there may also result a dishing phenomenon or a lining phenomenon due to the difference in the polishing rate between the insulation layer and the electrode wiring portions provided on the silicon substrate, and shortcircuiting between the through holes.
For obtaining a predetermined polishing rate in the mechanical and chemical polishing, it is necessary to maintain the polishing surface of the polishing pad always in satisfactory condition, by dressing the polishing surface, for example, with diamond particles.
In flattening the surface of the semiconductor apparatus by mechanical and chemical polishing, it is important to adequately manage the abrasion state of the polishing surface of the polishing pad, in order to always maintain the predetermined polishing rate.
The polishing pad can be of a type which has a high hardness and a high elasticity recovery rate and is used in the material requiring mechanical polishing such as an oxide film, or another type which has a low hardness and a high elasticity recovery rate and is used in the material requiring chemical polishing such as a polysilicon film, or a type of a two-layered pad structure, composed of the combination of the foregoing two types and having a high hardness and a high elasticity in the face contacting the wafer to be polished.
Because various types of such polishing pads are employed in the mechanical and chemical polishing, it has been extremely difficult to maintain constant surface conditions of the polishing surface of the polishing pad, thereby obtaining a predetermined polishing rate.
Conventionally, the timing of replacement of the polishing pad has been managed in time, in consideration of the frequency of use thereof. For this reason, the decrease of the polishing rate cannot be adequately judged promptly and there inevitably results a loss in the throughput.